Post on 19-Jul-2015
transcript
History
The abbreviation “CAN” stands for
“Controller Area Network”.
This bus:
• Introduced by Robert Bosch in 1986.
• Developed for automotive applications
• Standardized in 1993 as ISO11898-1
• CAN Standards :
• CAN 2.0A
• CAN 2.0B
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BUS topology
What is a Network Topology
It is the arrangement of various elements [Links, Nodes,
Etc.] for a Network [a telecommunication n/w] to
exchange Data
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Serial vs. Parrallel
Why Serial Communication
A few advantages
A serial connection requires fewer interconnecting cables (e.g.,
wires/ fibers) and hence occupies less space.
The extra space allows for better isolation of the channel from its
surroundings.
Serial is a better option because it is cheaper to implement
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CAN vs. MultiWire Network Physical medium – two wires terminated at both ends by resistors.
Differential signal - better noise immunity.
Benefits:
Reduced weight, Reduced cost
Fewer wires = Increased reliability
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Transmission Characteristics
Up to 1 Mbit/sec.
Common baud rates: 1 MHz, 500 KHz and 125 KHz
All nodes – same baud rate
Max length:120’ to 15000’ (rate dependent)
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Message Oriented Transmission
Protocol
Each node – receiver & transmitter
A sender of information transmits to all devices on the bus
All nodes read message, then decide if it is relevant to them
All nodes verify reception was error-free
All nodes acknowledge reception
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Bus Arbitration
Arbitration – needed when multiple nodes try to transmit at the
same time
Only one transmitter is allowed to transmit at a time.
A node waits for bus to become idle
Nodes with more important messages continue transmitting
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Bus Arbitration(2)
Message importance is encoded in message ID.
Lower value = More important
As a node transmits each bit, it verifies that it sees the same bit
value on the bus that it transmitted.
A “0” on the bus wins over a “1” on the bus.
Losing node stops transmitting, winner continues.
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A Basic CAN controller
Cheap CAN controller – CPU could get overrun with messages
even if it didn’t need them.
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